Re: [CAD_CAM_EDM_DRO] Re: How do I test IC SN74LS541N on PCB?

your octal (8-bit) tristate (the outputs can be
electronically disconnected) buffer (isolates a byte
from a bus) is TTL (transistor-transistor logic)
family of integrated circuits. it uses 5 volt supply.
on your particular chip:
2v and higher, on an input, is considered a logic
HIGH = 1 = v+ (or so)
0.8V and lower, on an input, is considered a logic LOW
= 0 = gnd (or so)
you can not harm an input by applying a voltage from
0-5v. the input will take very little current (mere
uA).

to test a chip manually on a protoboard:
wire all inputs to +5
wire the tristate enables to gnd
test each output to see that each is high.
then change all inputs to gnd and check outputs again.
then wire one enable to high.
all outputs should be dead off
wire the other enable to high
all outputs should be dead off.
this will not test all possible combinations but it is
the quickest preliminary way to check for a gross
failure. if it doesn't find a defect, and you are
halfway sure one of them IS defective, then just get a
whole batch of new ones and put in all new.

ok- that's been said; now to say how to do the job the
best way:
get a few new ics.
Program to fix board:

pull one ic
replace it with new.
WHILE !WORKIE
pull another IC
replace it with the one previously removed.
ENDWHILE



--- Bruce <bruce@...> wrote:

> The IC's are soldered in and I could plug the card
> in for testing but
> it would be very time consuming to get at all the
> chips.
> I am confident I can unsolder and solder in new
> chips, I have done
> this before but I figured the less I solder the less
> chance of
> damaging someting
> I have a very basic knowledge of electronic and when
> I looked at the
> datasheet on this chip I was lost.
> I thought one could bench test each chip one at a
> time by supplying
> the proper voltage 5 vdc and ground to the chip,
> supply the gate with
> high or low current then input 5 vdc to each input
> and checking the
> output to see if it is high or low depending one how
> the gate is set.
> Sounds like I was wrong on this part, but if it
> could be done, would
> supplying 5 vdc to the gate make it high and
> supplying nothing make it
> low? Would I supply the input with 5 vdc or nothing
> and check the
> output for high or low compared to what the gate is
> set for.
> Would I fry the chip if I put 5 vdc to the input,
> maybe I need to use
> a pulser, I have one although I am not positive how
> it works.
> The machine the board it out of is for hobby use so
> I have nothing to
> lose by trying to fix it myself.
> Clear as mud?
>
>
>
>
>
>
>
>
>
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